High pressure sodium vapor lamp having improved monolithic alumina arc tube

Abstract

A high pressure sodium vapor lamp contains a monolithic arc tube, the ends of which have a smaller inside diameter than has the body of the arc tube. Current-supply metal members are directly sealed in the ends of the arc tube.

I claim: 
     
       1. A high pressure sodium vapor lamp comprising a monolithic polycrystalline alumina arc tube having electrodes disposed at the ends thereof and containing a fill including sodium, mercury and inert gas, said arc tube consisting of a tubular body portion and two end portions, the outside diameter of said end portions being smaller than the outside diameter of said body portion, there being no sealing region between said end portion and said body portion, said body portion having a uniform inside diameter throughout its length, each of said end portions having an axial hole therethrough, the diameter of said axial hole being smaller than the inside diameter of the body portion, cylindrical metallic members extending through and sealed to said end portions, said electrodes being supported on metal rods extending from the internal ends of said metallic members. 
     
     
       2. The lamp of claim 1 wherein said metallic member is a niobium tube sealed at its internal end. 
     
     
       3. The lamp of claim 1 wherein the diameter of said axial hole exceeds only slightly the diameter of said electrode.